/**
 * SMTP Data Handler
 * Responsible for processing email data during and after DATA command
 */

import * as plugins from '../../../plugins.js';
import * as fs from 'fs';
import * as path from 'path';
import { SmtpState } from './interfaces.js';
import type { ISmtpSession, ISmtpTransactionResult } from './interfaces.js';
import type { IDataHandler, ISessionManager } from './interfaces.js';
import { SmtpResponseCode, SMTP_PATTERNS, SMTP_DEFAULTS } from './constants.js';
import { SmtpLogger } from './utils/logging.js';
import { Email } from '../../core/classes.email.js';
import { UnifiedEmailServer } from '../../routing/classes.unified.email.server.js';

/**
 * Handles SMTP DATA command and email data processing
 */
export class DataHandler implements IDataHandler {
  /**
   * Session manager instance
   */
  private sessionManager: ISessionManager;
  
  /**
   * Email server reference
   */
  private emailServer: UnifiedEmailServer;
  
  /**
   * SMTP server options
   */
  private options: {
    size: number;
    tempDir?: string;
    hostname?: string;
  };
  
  /**
   * Creates a new data handler
   * @param sessionManager - Session manager instance
   * @param emailServer - Email server reference
   * @param options - Data handler options
   */
  constructor(
    sessionManager: ISessionManager,
    emailServer: UnifiedEmailServer,
    options: {
      size?: number;
      tempDir?: string;
      hostname?: string;
    } = {}
  ) {
    this.sessionManager = sessionManager;
    this.emailServer = emailServer;
    
    this.options = {
      size: options.size || SMTP_DEFAULTS.MAX_MESSAGE_SIZE,
      tempDir: options.tempDir,
      hostname: options.hostname || SMTP_DEFAULTS.HOSTNAME
    };
    
    // Create temp directory if specified and doesn't exist
    if (this.options.tempDir) {
      try {
        if (!fs.existsSync(this.options.tempDir)) {
          fs.mkdirSync(this.options.tempDir, { recursive: true });
        }
      } catch (error) {
        SmtpLogger.error(`Failed to create temp directory: ${error instanceof Error ? error.message : String(error)}`, {
          error: error instanceof Error ? error : new Error(String(error)),
          tempDir: this.options.tempDir
        });
        this.options.tempDir = undefined;
      }
    }
  }
  
  /**
   * Process incoming email data
   * @param socket - Client socket
   * @param data - Data chunk
   * @returns Promise that resolves when the data is processed
   */
  public async processEmailData(socket: plugins.net.Socket | plugins.tls.TLSSocket, data: string): Promise<void> {
    // Get the session for this socket
    const session = this.sessionManager.getSession(socket);
    if (!session) {
      this.sendResponse(socket, `${SmtpResponseCode.LOCAL_ERROR} Internal server error - session not found`);
      return;
    }
    
    // Clear any existing timeout and set a new one
    if (session.dataTimeoutId) {
      clearTimeout(session.dataTimeoutId);
    }
    
    session.dataTimeoutId = setTimeout(() => {
      if (session.state === SmtpState.DATA_RECEIVING) {
        SmtpLogger.warn(`DATA timeout for session ${session.id}`, { sessionId: session.id });
        this.sendResponse(socket, `${SmtpResponseCode.LOCAL_ERROR} Data timeout`);
        this.resetSession(session);
      }
    }, SMTP_DEFAULTS.DATA_TIMEOUT);
    
    // Update activity timestamp
    this.sessionManager.updateSessionActivity(session);
    
    // Store data in chunks for better memory efficiency
    if (!session.emailDataChunks) {
      session.emailDataChunks = [];
    }
    
    session.emailDataChunks.push(data);
    
    // Check if we've reached the max size
    let totalSize = 0;
    for (const chunk of session.emailDataChunks) {
      totalSize += chunk.length;
    }
    
    if (totalSize > this.options.size) {
      SmtpLogger.warn(`Message size exceeds limit for session ${session.id}`, { 
        sessionId: session.id,
        size: totalSize,
        limit: this.options.size
      });
      
      this.sendResponse(socket, `${SmtpResponseCode.EXCEEDED_STORAGE} Message too big, size limit is ${this.options.size} bytes`);
      this.resetSession(session);
      return;
    }
    
    // Check for end of data marker - combine all chunks to ensure we don't miss it if split across chunks
    const combinedData = session.emailDataChunks.join('');
    
    // More permissive check for the end-of-data marker
    // Check for various formats: \r\n.\r\n, \n.\r\n, \r\n.\n, \n.\n, or just . or .\r\n at the end
    if (combinedData.endsWith('\r\n.\r\n') || 
        combinedData.endsWith('\n.\r\n') || 
        combinedData.endsWith('\r\n.\n') || 
        combinedData.endsWith('\n.\n') || 
        data === '.\r\n' || 
        data === '.') {
      
      SmtpLogger.debug(`End of data marker found for session ${session.id}`, { sessionId: session.id });
      
      // End of data marker found
      await this.handleEndOfData(socket, session);
    }
  }
  
  /**
   * Process a complete email
   * @param session - SMTP session
   * @returns Promise that resolves with the result of the transaction
   */
  public async processEmail(session: ISmtpSession): Promise<ISmtpTransactionResult> {
    // Combine all chunks and remove end of data marker
    session.emailData = (session.emailDataChunks || []).join('');
    
    // Remove trailing end-of-data marker: various formats
    session.emailData = session.emailData
      .replace(/\r\n\.\r\n$/, '')
      .replace(/\n\.\r\n$/, '')
      .replace(/\r\n\.\n$/, '')
      .replace(/\n\.\n$/, '')
      .replace(/\.$/, '');  // Handle a lone dot at the end
    
    // Remove dot-stuffing (RFC 5321, section 4.5.2)
    session.emailData = session.emailData.replace(/\r\n\.\./g, '\r\n.');
    
    try {
      // Parse email into Email object
      const email = await this.parseEmail(session);
      
      // Process the email based on the processing mode
      const processingMode = session.processingMode || 'mta';
      
      let result: ISmtpTransactionResult = {
        success: false,
        error: 'Email processing failed'
      };
      
      switch (processingMode) {
        case 'mta':
          // Process through the MTA system
          try {
            SmtpLogger.debug(`Processing email in MTA mode for session ${session.id}`, { 
              sessionId: session.id,
              messageId: email.getMessageId()
            });
            
            // Generate a message ID since queueEmail is not available
            const messageId = `${Date.now()}-${Math.floor(Math.random() * 1000000)}@${this.options.hostname || 'mail.example.com'}`;
            
            // In a full implementation, the email would be queued to the delivery system
            // await this.emailServer.queueEmail(email);
            
            result = {
              success: true,
              messageId,
              email
            };
          } catch (error) {
            SmtpLogger.error(`Failed to queue email: ${error instanceof Error ? error.message : String(error)}`, { 
              sessionId: session.id,
              error: error instanceof Error ? error : new Error(String(error))
            });
            
            result = {
              success: false,
              error: `Failed to queue email: ${error instanceof Error ? error.message : String(error)}`
            };
          }
          break;
          
        case 'forward':
          // Forward email to another server
          SmtpLogger.debug(`Processing email in FORWARD mode for session ${session.id}`, { 
            sessionId: session.id,
            messageId: email.getMessageId()
          });
          
          // Forward logic would be implemented here
          result = {
            success: true,
            messageId: email.getMessageId(),
            email
          };
          break;
          
        case 'process':
          // Process the email immediately
          SmtpLogger.debug(`Processing email in PROCESS mode for session ${session.id}`, { 
            sessionId: session.id,
            messageId: email.getMessageId()
          });
          
          // Direct processing logic would be implemented here
          result = {
            success: true,
            messageId: email.getMessageId(),
            email
          };
          break;
          
        default:
          SmtpLogger.warn(`Unknown processing mode: ${processingMode}`, { sessionId: session.id });
          result = {
            success: false,
            error: `Unknown processing mode: ${processingMode}`
          };
      }
      
      return result;
    } catch (error) {
      SmtpLogger.error(`Failed to parse email: ${error instanceof Error ? error.message : String(error)}`, { 
        sessionId: session.id,
        error: error instanceof Error ? error : new Error(String(error))
      });
      
      return {
        success: false,
        error: `Failed to parse email: ${error instanceof Error ? error.message : String(error)}`
      };
    }
  }
  
  /**
   * Save an email to disk
   * @param session - SMTP session
   */
  public saveEmail(session: ISmtpSession): void {
    if (!this.options.tempDir) {
      return;
    }
    
    try {
      const timestamp = Date.now();
      const filename = `${session.id}-${timestamp}.eml`;
      const filePath = path.join(this.options.tempDir, filename);
      
      fs.writeFileSync(filePath, session.emailData);
      
      SmtpLogger.debug(`Saved email to disk: ${filePath}`, { 
        sessionId: session.id,
        filePath
      });
    } catch (error) {
      SmtpLogger.error(`Failed to save email to disk: ${error instanceof Error ? error.message : String(error)}`, { 
        sessionId: session.id,
        error: error instanceof Error ? error : new Error(String(error))
      });
    }
  }
  
  /**
   * Parse an email into an Email object
   * @param session - SMTP session
   * @returns Promise that resolves with the parsed Email object
   */
  public async parseEmail(session: ISmtpSession): Promise<Email> {
    // Parse raw email text to extract headers
    const rawData = session.emailData;
    const headerEndIndex = rawData.indexOf('\r\n\r\n');
    
    if (headerEndIndex === -1) {
      // No headers/body separation, create basic email
      return new Email({
        from: session.envelope.mailFrom.address,
        to: session.envelope.rcptTo.map(r => r.address),
        subject: 'Received via SMTP',
        text: rawData
      });
    }
    
    // Extract headers and body
    const headersText = rawData.substring(0, headerEndIndex);
    const bodyText = rawData.substring(headerEndIndex + 4); // Skip the \r\n\r\n separator
    
    // Parse headers
    const headers: Record<string, string> = {};
    const headerLines = headersText.split('\r\n');
    let currentHeader = '';
    
    for (const line of headerLines) {
      // Check if this is a continuation of a previous header
      if (line.startsWith(' ') || line.startsWith('\t')) {
        if (currentHeader) {
          headers[currentHeader] += ' ' + line.trim();
        }
        continue;
      }
      
      // This is a new header
      const separatorIndex = line.indexOf(':');
      if (separatorIndex !== -1) {
        const name = line.substring(0, separatorIndex).trim().toLowerCase();
        const value = line.substring(separatorIndex + 1).trim();
        headers[name] = value;
        currentHeader = name;
      }
    }
    
    // Extract common headers
    const subject = headers['subject'] || 'No Subject';
    const from = headers['from'] || session.envelope.mailFrom.address;
    const to = headers['to'] || session.envelope.rcptTo.map(r => r.address).join(', ');
    const messageId = headers['message-id'] || `<${Date.now()}.${Math.random().toString(36).substring(2)}@${this.options.hostname}>`;
    
    // Create email object
    const email = new Email({
      from: from,
      to: to.split(',').map(addr => addr.trim()),
      subject: subject,
      text: bodyText,
      // Add original session envelope data for accurate routing as headers
      headers: {
        'X-Original-Mail-From': session.envelope.mailFrom.address,
        'X-Original-Rcpt-To': session.envelope.rcptTo.map(r => r.address).join(', '),
        'Message-Id': messageId
      }
    });
    
    // Add received header
    const timestamp = new Date().toUTCString();
    const receivedHeader = `from ${session.clientHostname || 'unknown'} (${session.remoteAddress}) by ${this.options.hostname} with ESMTP id ${session.id}; ${timestamp}`;
    email.addHeader('Received', receivedHeader);
    
    // Add all original headers
    for (const [name, value] of Object.entries(headers)) {
      if (!['from', 'to', 'subject', 'message-id'].includes(name)) {
        email.addHeader(name, value);
      }
    }
    
    return email;
  }
  
  /**
   * Handle end of data marker received
   * @param socket - Client socket
   * @param session - SMTP session
   */
  private async handleEndOfData(socket: plugins.net.Socket | plugins.tls.TLSSocket, session: ISmtpSession): Promise<void> {
    // Clear the data timeout
    if (session.dataTimeoutId) {
      clearTimeout(session.dataTimeoutId);
      session.dataTimeoutId = undefined;
    }
    
    try {
      // Update session state
      this.sessionManager.updateSessionState(session, SmtpState.FINISHED);
      
      // Optionally save email to disk
      this.saveEmail(session);
      
      // Process the email
      const result = await this.processEmail(session);
      
      if (result.success) {
        // Send success response
        this.sendResponse(socket, `${SmtpResponseCode.OK} OK message queued as ${result.messageId}`);
      } else {
        // Send error response
        this.sendResponse(socket, `${SmtpResponseCode.TRANSACTION_FAILED} Failed to process email: ${result.error}`);
      }
      
      // Reset session for new transaction
      this.resetSession(session);
    } catch (error) {
      SmtpLogger.error(`Error processing email: ${error instanceof Error ? error.message : String(error)}`, { 
        sessionId: session.id,
        error: error instanceof Error ? error : new Error(String(error))
      });
      
      this.sendResponse(socket, `${SmtpResponseCode.LOCAL_ERROR} Error processing email: ${error instanceof Error ? error.message : String(error)}`);
      this.resetSession(session);
    }
  }
  
  /**
   * Reset session after email processing
   * @param session - SMTP session
   */
  private resetSession(session: ISmtpSession): void {
    // Clear any data timeout
    if (session.dataTimeoutId) {
      clearTimeout(session.dataTimeoutId);
      session.dataTimeoutId = undefined;
    }
    
    // Reset data fields but keep authentication state
    session.mailFrom = '';
    session.rcptTo = [];
    session.emailData = '';
    session.emailDataChunks = [];
    session.envelope = {
      mailFrom: { address: '', args: {} },
      rcptTo: []
    };
    
    // Reset state to after EHLO
    this.sessionManager.updateSessionState(session, SmtpState.AFTER_EHLO);
  }
  
  /**
   * Send a response to the client
   * @param socket - Client socket
   * @param response - Response message
   */
  private sendResponse(socket: plugins.net.Socket | plugins.tls.TLSSocket, response: string): void {
    try {
      socket.write(`${response}${SMTP_DEFAULTS.CRLF}`);
      SmtpLogger.logResponse(response, socket);
    } catch (error) {
      // Attempt to recover from specific transient errors
      if (this.isRecoverableSocketError(error)) {
        this.handleSocketError(socket, error, response);
      } else {
        // Log error for non-recoverable errors
        SmtpLogger.error(`Error sending response: ${error instanceof Error ? error.message : String(error)}`, {
          response,
          remoteAddress: socket.remoteAddress,
          remotePort: socket.remotePort,
          error: error instanceof Error ? error : new Error(String(error))
        });
      }
    }
  }
  
  /**
   * Check if a socket error is potentially recoverable
   * @param error - The error that occurred
   * @returns Whether the error is potentially recoverable
   */
  private isRecoverableSocketError(error: unknown): boolean {
    const recoverableErrorCodes = [
      'EPIPE',       // Broken pipe
      'ECONNRESET',  // Connection reset by peer
      'ETIMEDOUT',   // Connection timed out
      'ECONNABORTED' // Connection aborted
    ];
    
    return (
      error instanceof Error && 
      'code' in error && 
      typeof (error as any).code === 'string' && 
      recoverableErrorCodes.includes((error as any).code)
    );
  }
  
  /**
   * Handle recoverable socket errors with retry logic
   * @param socket - Client socket
   * @param error - The error that occurred
   * @param response - The response that failed to send
   */
  private handleSocketError(socket: plugins.net.Socket | plugins.tls.TLSSocket, error: unknown, response: string): void {
    // Get the session for this socket
    const session = this.sessionManager.getSession(socket);
    if (!session) {
      SmtpLogger.error(`Session not found when handling socket error`);
      if (!socket.destroyed) {
        socket.destroy();
      }
      return;
    }
    
    // Get error details for logging
    const errorMessage = error instanceof Error ? error.message : String(error);
    const errorCode = error instanceof Error && 'code' in error ? (error as any).code : 'UNKNOWN';
    
    SmtpLogger.warn(`Recoverable socket error during data handling (${errorCode}): ${errorMessage}`, {
      sessionId: session.id,
      remoteAddress: session.remoteAddress,
      error: error instanceof Error ? error : new Error(String(error))
    });
    
    // Check if socket is already destroyed
    if (socket.destroyed) {
      SmtpLogger.info(`Socket already destroyed, cannot retry data operation`);
      return;
    }
    
    // Check if socket is writeable
    if (!socket.writable) {
      SmtpLogger.info(`Socket no longer writable, aborting data recovery attempt`);
      if (!socket.destroyed) {
        socket.destroy();
      }
      return;
    }
    
    // Attempt to retry the write operation after a short delay
    setTimeout(() => {
      try {
        if (!socket.destroyed && socket.writable) {
          socket.write(`${response}${SMTP_DEFAULTS.CRLF}`);
          SmtpLogger.info(`Successfully retried data send operation after error`);
        } else {
          SmtpLogger.warn(`Socket no longer available for data retry`);
          if (!socket.destroyed) {
            socket.destroy();
          }
        }
      } catch (retryError) {
        SmtpLogger.error(`Data retry attempt failed: ${retryError instanceof Error ? retryError.message : String(retryError)}`);
        if (!socket.destroyed) {
          socket.destroy();
        }
      }
    }, 100); // Short delay before retry
    }
  }